The present invention is directed to a storage stable aqueous composition of silica fume and an alkali metal nitrite. The present composition is useful as a cement admixture to provide enhanced compressive strength and impart corrosion resistance to the resultant concrete structure.
Specifically, the present invention is directed to a storage stable aqueous composition containing silica fume, and metal nitrite salt with at least a stabilizing amount of an alkylene glycol or oxyalkylene glycol. The composition imparts the desired properties of enhanced compressive strength and corrosion inhibition to cement compositions, such as mortar and concrete.
It has been known that silicious material such as fume silica can impart enhanced strength to cement compositions when made part of its formulation. It has also been known that alkali and alkaline earth metal nitrites, such as calcium nitrite, can impart set acceleration and corrosion resistance with respect to the metal elements contained in the treated concrete formations.
It would be desirable to have a single cement admixture composition which cn be applied at the job site to provide both of these additive materials for their known purpose. However, when one has previously attempted to incorporate a metal nitrite salt, such as calcium nitrite, into aqueous silica fume dispersions, one causes the dispersion to produce a hard gel product. Such products are not suitable for use as an admixture which can be readily applied at the job site.
It has been unexpectedly found that when a water soluble alkylene glycol or oxyalkylene glycol, as fully described below, is present, one obtains a stable, fluid, aqueous dispersion of silica fume and alkali metal nitrite. Further, if the glycol is present in certain amounts, the subject admixture further provides inhibition of drying shrinkage to the treated cement composition.
Hydraulic cement compositions, such as mortar (cement, small particulate, e.g. sand, and water), or concrete (cement, small particulate, large particulate, e.g. gravel, and water), have certain properties which substantially effect their durability. The properties of compressive strength, corrosion inhibition of metal members and lack of cracks and other defects due to shrinkage which occurs during drying of the cured structural member are highly desired.
One of the main advantages of using concrete compositions, to form architectural structural members is their ability to be cast into a desired form which is capable of exhibiting high compressive strength. With increased strength, the concrete can bear greater loads or be used to form smaller members capable of bearing equal loads to its non-treated counterpart.
It is highly desired to provide a cement admixture which is capable of inhibiting corrosion of metal reinforcing elements in structural concrete compositions while enhancing the compressive strength of the resultant cured structure.
Alkylene glycols and glycerols have been used in combination with cement compositions for particular purposes. For example, these materials have been added to inhibit water crystal formation when casting in cold climate conditions or to inhibit the rate of evaporation of water in cement slurries used in high temperature well bore hole applications. Further, these additives have been used to provide a layer above cast, unset composition to inhibit evaporation of water at the surface portion of the structure and thereby enhancing the hydration of the cement at that portion of the formation.
It is highly desirable to have a single admixture composition which is capable of providing both enhanced compressive strength and corrosion inhibition and which is a storage stable, flowable, uniform aqueous dispersion. It is further desirable to provide a single storage stable, uniform admixture composition which provides enhanced compressive strength, corrosion inhibition and reduced drying shrinkage.